1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, an MFP, a facsimile, or a multifunction device thereof, and a method for detecting a separated state of a transfer member in the image forming apparatus. The present invention can be utilized, for example, for detecting a pressed or separated state of a secondary transfer roller with respect to an intermediate transfer belt.
2. Description of the Prior Art
Conventionally, an image forming apparatus that is called an electrophotographic type copying machine, a printer, a facsimile, a multiple function processor or an MFP (Multi Function Peripherals) forms images by developing an electrostatic latent image formed on a photosensitive drum so as to form a toner image, which is transferred to an intermediate transfer belt as a primary transfer and further transferred to a paper sheet as a secondary transfer, which is fixed. In order to perform the secondary transfer of the toner image from the intermediate transfer belt to the paper sheet, there is provided a secondary transfer roller that becomes a pressed state with respect to the intermediate transfer belt that is an image carrier.
In this image forming apparatus, the secondary transfer roller can move with respect to the intermediate transfer belt between the pressed state and the separated state. Although the secondary transfer roller is in the pressed state in a normal image forming (printing) state, it is normally in the separated state while the image forming process is not performed.
In another conventional structure, a test toner patch is formed on an intermediate transfer belt, and a state of the toner patch is detected by an IDC sensor so that conditions for forming an image are adjusted. In this case too, the secondary transfer roller is set to be in the separated state so that the secondary transfer roller or the like does not become dirty with the toner.
Furthermore, a press and separation driving device is provided for moving the secondary transfer roller, and an optical sensor such as a photointerrupter is used for detecting whether or not the secondary transfer roller is switched securely to the separated state or the pressed state by the press and separation driving device.
However, if the photointerrupter is used for detecting the pressed state and the separated state, the number of components increases, and it causes increase of cost. On the other hand, Japanese unexamined patent publication No. 2004-264455 discloses a device that does not include a special-purpose photointerrupter, but a photointerrupter for use of detecting a paper jam is also used for the above-mentioned purpose.
However, a single photointerrupter is shared for detecting timings of paper arrival and pass and for detecting the pressed or separated state of the secondary transfer roller in the above-mentioned conventional device. Therefore, it is necessary to use a special pre-transfer sensor flag for detecting arrival and pass timings of a paper sheet, so an operation of detecting a paper jam or the like may be subject to some constraints.